Chitosan is a highly insoluble N-acetylated polymer of beta-(1,4)-D-glucosamine with a pyranose unit and a biopolymer with a high molecular weight over 1 million Daltons bonded to a functional group of glucosamine over 5,000 units. Chitosan is a cellulose-like polymer present in fungal walls and the exoskeletons of arthropods, including insects, crabs, shrimps, and lobsters. Chitosan having a structural unit similar to cellulose can be applied in numerous fields of medical industry, due to its high bioavailability and a negative effect against immune response. Ever since the FDA (of the U.S.) recognized chitosan as a food additive, chitosan has been applied to biological engineering as an essential biomedical material.
For example, chitosan can be used in various industrial applications, including wastewater treatment (as a coagulant agent, heavy-metal absorbent, and waste-dye clarifier) and uses in the agricultural industry (as a soil-conditioner insecticide, plant antiviral agent, and agricultural chemical agent).
Lately, as the chitosan is known to have a molecular weight of 20,000˜100,000 with a highly physical activity, the applications of chitosan were extended to include the practical fields of foods and beverages, health and sanitation, cosmetics, textiles, and medicines. The solubility and viscosity of chitosan are considered major problematic matters in such applications, since the chitosan is water-immiscible and grows viscous even when dissolved in water. Therefore, there is an urgent need to provide water-soluble chitosan free of the above problems.
Water-soluble chitosan has received considerable attention in this context since it can be applied to the aforementioned practical fields.
In the food industry, especially in health food, water-soluble chitosan shows various physical properties, including cholesterol reduction, enhanced immune response, improved liver function, absorption in the alimentary canal, and the control of blood sugar level and blood pressure. Additionally, chitosan's unique abilities, such as removal of skin-waste, excellent heat conservation, moisturization, antibacterial activity, and activation of cutaneous cells, have resulted in its employment as a primary component in the cosmetic industry, in such products as shampoo, hair rinse, hair spray, hair gel, creams, bathing agents, face packs, and face-washing agents. Moreover, the water-solubility of the chitosan is necessary for applications of products administered in a spray form, so that the chitosan can easily penetrate the wall of inner cutaneous cells and to prevent an increase in viscosity.
Additionally, the water-soluble chitosan is useful as a drug carrier such as an osteoporosis agent, an antirheumatism treating agent, and a heavy-metal removal agent, which can act in vivo, essentially with a high biological activity and water-solubility. As a drug carrier, the water-soluble chitosan is prepared in a variety of forms including tablets, capsules, pills, suspensions, solutions, and emulsions administered orally and parenterally.
Due to the presence of a strong hydrogen bond among adjacent atoms in chitosan, however, strong acid including organic acids (such as lactic acid, acetic acid, propionic acid, and tartaric acid) and inorganic acids (such as hydrochloric acid, nitric acid, and sulfuric acid) are required to dissolve the chitosan. Meanwhile, the toxicity of such strong acids raises still another problem to be applied in medical fields.
There are two different methods to prepare water-soluble chitosan: a chemical method and an enzymatic method.
In the chemical method, it is suggested that the water-soluble chitosan is prepared by hydrolysis using hydrochloric acid. This method, however, requires excessive amounts of HCl and an overly long period of time to hydrolyze the chitosan. As an another known chemical method, it is also suggested that the water-soluble chitosan is obtained by substitution of amine moiety at the C-2 position of chitosan with another moiety or by forming amine salt such as —NH3+.CH3CHOHCOO−, —NH3+.CH3COO—, —NH3+.Cl−, —NH3+.CH3CH2COO−, —NH3+.HCOO−, or —NH3+. .HOOC(CHOH2)COO−. This process has an advantage in that the water-soluble chitosan prepared does not further reduce molecular weight so that can be generally used in this art. The water-soluble chitosan obtained by this process, however, has a disadvantage in that it is difficult to dissolve in a gastro-instestinal tract of pH 1.2˜1.5, because the aqueous solution containing chitosan salt shows pH 3.0 based on a 1.0% solution.
On the contrary, in the enzymatic method, the water-soluble is prepared by enzymatic treatment comprising steps of: dissolving chitosan in poor acid solution; hydrolyzing by enzymatic treatment about for 24 hours; and freeze-drying followed by packaging. Since the drying procedure is carried out without additional purification, the final product, which contains acid, can create problems when administered due to the acid's toxicity.
Hence, there is a need for method preparing water-soluble chitosan to solve the aforementioned problems, namely, for effective removal of leftover impurities and acid salt. As one attempt to realize such a method, Korea Patent No. 2000-15959 discloses a method for the removal of leftover salt and the unpleasant odor, comprising enzymolysis followed by forming an aqueous chitosan oligo sugar solution and passing the obtained solution through anionic exchange resin. The above disclosure, however, neither describes nor suggests properties of chitosan with high purity.
Therefore, the present invention contrives to realize water-soluble chitosan with high biological activity and high purity, one that is suitable for biomedical engineering applications.